Electric sphygmometer



Aug. 1, 1944, H. R. L-IPPlTT ELECTRIC SPHYGMOMETER- Filed NOV. l, 194-1.H' @7419 R. ijpi/ifi;

ew A I UNITED STATES PATE ELECTRIC srnrGMoMsTEn Harry R. Lippitt, NewYork, N. Y.

Application November 1, 1941, sci-n1 No. 417,549

4 Claims. 12 8-2.05)

This invention relates to an electric sphygmometer and more particularlyto an improved arrangement for measuring and indicating the strength oithe pulse beat and the utilization thereoi as an adjunct to asphygmomanometer for obtaining accurate systolic and diastolic bloodpressure readings.

It is the object of the present invention to provide a sensitivearrangement for indicating with exactitude the incidence of. thesystolic and diastolic blood pressures in order that the read ings onthesphygmomanometer may be noted at such times with no guesswork.

It is the obiec'tof the present invention to prowhich aresubject toerrors occasioned by extraneous vibrations or by the defective oruncertain hearing or scope.

Thepresentinvention roceeds upon the principle oi providing'a crystalmicrophone in lieu of the stethoscope which is usually employed in themeasuring of blood pressures, which microphone is characterized by highsensitivity. The

the operator or the stethoelectrical indicating instrument which clearlyand visibly vibrates corresponding to the vibrations imposed upon thecrystal microphone.

The pressure is applied until no regular vibrations are recorded on theelectrical indicating instrument. The air is then gradually permitted 1to escape from'the cufl until the pulse again causes the mechanicalvibration of the crystal microphone. The reading at this point on thecircular scale or column of. mercury of the sp y momanometer indicates.the systolic pressure or the highest pressure in the arteries during thecontraction of the heart. The deflation of the out! is continued andthat point on the scale when the last vibrations of the disappearingpulse is imposed upon the crystal microphone and is translated intothevibrations of the indicating instrument at the output of the ampli fyingunit, is the diastolic pressure or the lowest pressure in the arteriesduring diastole or relaxation of the heart muscle between beats.

Thus, the pulse variations which are applied to the sphygmometer areindicated positively by the action of the pulse alone withoutinterference 'of any other extraneous body vibrations or vibrationsinthe room in which the testing operation is being undertaken, andwithout possibility of mistaking the points at which the relativeintensitiesof the pulse beats undergo marked changes. v Other objectsand purposes of the invention 'will appear from' the following detaileddesphygmomanometer used in conjunction with the I crystal microphone maybe of any conventional ype'the scale readings'or which may be noted on acolumn oi'mercury, or on a circular dial. In sucharrangements, a rubberbag cufl is wrapped around the upper arm and is inflated by a hand bulb.This cut! may be connected by rubbertubing to a sphygmomanomete'r ormeasing device in the form or a sealed column of mere cury. Inaccordance with the present invention, the crystal microphone'is appliedover the artery below the cut! and pressure is applied by pumping airinto the rubber cut! to compress the brachial artery in the uppelfarm."As the pressure is applied, the pulse; causes mechanical scription ofthe invention following hereinafter taken-in conjunction with theaccompanying drawing, wherein is shown one preferred mode of executionthereof.

As shown in the drawing, the sphygmomanometer i0 is exemplified by asealed column of mercury ll adjacent to a suitable scale I2; The columnof mercury is connected to the rubber .cufl l5 through the intermediaryof the rubber tubing 13. The cuff I5 is adapted to be inflatedvibrations of the crystal microphone which are translated intoelectrical variations which are imposed upon a inulti-stage amplifyingunit, at

the output 01' which is preter'ablydisposed an by the hand bulb it whichis also provided with means for allowing the air to escape gradually in'a manner well known in the art 01' such devices.

The sphygmometer or indicating device adapted to be used in conjunctionwith this sphy momanometer I0 is illustrated schematically in thedrawing and'essentially consists of a 'crystalmicrophone 20 at the inputof thedevice which is designed to have impressed thereupon thepulse-beats, the vibrations of which are am'-- plifled by means oithermionic amplifiers to give a visible indication oi the vibrations"corresponding to those impressed'upon the microphone at -transforming'mechanical pressures output of the amplifier on the galvanometerinstrument G, the needle of which will swing correspondingly to thevibrations impressed on the crystal microphone.

The crystal microphone .2. comprises a vibratile crystal havingcharacteristic capability of imposed thereupon into electricalvariations. These electrical variations are amplified through aplurality of amplifying stages to give a visible indica- I tion whichreliably indicates the pulse vibrations. This represents a markedimprovement over the aural indications normally obtained by the use of astethoscope. Although various arrangements may be devised for theamplification of the electrical variations produced by microphone,

I have found the one illustrated in, the drawing to be highly sensitiveand productive of excellent results. Y

The conductor leading from the microphone I! to the amplifier isenclosed in' a sheathed cable 2| which is suitably grounded. A variableresistor R1 operates as a variable gain control which is coupled to theinput of the 'first amplifier V1 through capacity C1 and resistor R2..The amplifier V1 may be a miniature type diode-pentode which isdesignated commercially as the 185 tube. The diode element in the tubeis connected to the filament and the tube in the present installationfunctions merely as an audio frequency pentode characterized by a highgain.-

sistor R4 is connected with conductor ll and cond-uctors 25, 28, 21 and2a to the positive terminal of the B supply 30, which may be of -45 or67.5 volts, to impose the necessary positive potential on thatamplifier. The resistor R: in series with the screen grid 4 reduces thepositive potential applied to that element by the necessary amount,which resistor is by-passed by the condenser C2,

which operates as a decoupling medium to exclude any variable effectsupon the plate supply occasioned by the audio frequencies in theamplifiercircuit.

The second stage of amplification is similar to the first and theamplifier Va is likewise of the 155 type. The plate I in this stage isenergized from theplate supply ll through the conductor SI, resistor Ra,conductors Ii, 21 and II and plate supply II. The screen grid potentialis likewise reduced by the resistor Re which is by-passed by condenserC: functioning in the'same manner as above.

The output from the second stage of amplification flowing throughconductor 32 is impressed 'at point ll on condensers Cs and- C-i inorder to capacitively couple the. output of the tube V: with the inputsof the tubes V: and V4 which are arranged in parallel. These tubes areminiature type power amplifier 'pentodes designated commercially as the154 type, which are characterised by high efilciency and'good powersensitivity. Th seven terminals of the ampliflersvs-and Vs aredesignated in the drawing according to .75

standard practice, except that these are primed in order, to distinguishthem from the terminals of the amplifiers V1 and V:.- The energy whichis impressed across the grids 3' in parallel is amplified by the tubesand appears in the output circuit connected with the plates 2' inconductor 82, in which is disposed the primary winding 41 of audiotransformer T. The secondary winding 48 of this transformer has incircuit therewith the electrical indicating instrument G which serves toindicate visibly the variations which are imposed upon the microphone inthe input circuit.

The electrical connections for energizing the circuits .are completed bythe closing of a switch 4| which operates to complete the circuit forenergizing the filaments of the several tubes through conductor ii, theA supply I0 and ground. This switch ll also completes the connectionsfor the "3 supply II to the various plates and screen grids. A resistorRs, which may be 3 megohms, is provided in conductor ll which isconnected to the grids of tubes V3 and V4 and operates as a grid leak.The resistor R1 serves to impose the Proper bias on the grids of thelast two amplifiers'with respectto the ground. Condensers C4 and Cs oflarge capacity may be electrolytic condensers.

I found the following values applied to the various elements to resultin a highly satisfactory and sensitive amplifying arrangement:

m=5 megohms Rs, Rs=l0 megohms R1. R0, Rs==3 megohms Rs, Ro=% to 1 megohmR1=1000 ohms C1=0.001 mfd.

Cs=0.l to 1 mfd. Cs=0.1 tol mfd.

04:10 mfd.

Cs=0.005 mfd. C1=0.001 mfd. Cs=0.001 mfd.

' The "A" supply for the tubes, 50, consists of a 1.4 volt cell whilethe "B" supply may be 67 to volts. I have found an audio transformerparticularly suitable in whichthe primary winding I has a resistance of700 ohms while the seconds-W winding resistance is l to 2 ohms. Theindicating instrument G is referably a DArsonval galvanometer having acapacity of 0 to v to 200 -=microamperes. The indications are alsoobtainable by the use of a millivoitmeter. Dry rectifiers may be used inthe indicating circuit.

While I have shown my sphygmometer particularly adapted for use as anadjunct to the measuring of blood pressures in association with asphygmomanometer, the same may be found useful in other applicationswhere a sensitive instrument is desired for the measuring of thestrength of the pulse beats. The crystal microphone described hereinutilizes a piezo-electric crystal, but any device characterized by thesame behavior or which has the capability of transforming a mechanicalstress to an electrical variation may be employed.

While I have described my invention as embodiedin a specific form and asoperating in' a specific manner for purposes of illustration, it shouldbe understood that I do not limit my invention thereto, sincevariousmodifications will s est tothose (skilled in the without departing fromthe spirit or my invention, the scope of which is set forth in" theannexed claims.

I claim:

1. In combination with a sphygmomanometer for measuring blood pressure,a sphygmometer for indicating pulse beats which comprises a crystalmicrophone adapted to be placed in contact with a person in closeproximity to an artery and to be subjected to the pulse vibrations, apair of successive resistance-coupled thermionic amplifying stagesconnected with said microphone for amplitying the electrical variationsproduced by the pulse vibrations acting on said crystal microphonecomprising two successive miniature type audiofrequency pentode tubes, apair of miniature type power-output pentodes connected in parallel andadapted to amplify further the output energy from said first stages, andan electric meter connected to the output of said last-mentionedpentodes for visibly indicating the pulse beat vibrations by thevariations of the readings registered on said electric meter.

2. In combination with a sphvgmomanometer for measuring blood pressure,a sphygmometer for indicating pulse beats which comprises a crystalmicrophone adapted to be placed in contact with a person in closeproximity to an artery and to be subjected tosthe pulse vibrations, aplurality of thermionic amplifying stages connected to said microphone,and an indicating device at the output of said amplifying stages forclearly and visibly indicating the points at which the systolicsphygmometer.

and diastolic blood pressure readings on "the 'sphygmomanometer shouldbe noted correspondw microphone, and an electric meter connected at theoutput of said amplifying stages for visibly indicating the pulse beatvibrations by the variations of the readings registered on said electricmeter whereby is indicated the points at which the systolic anddiastolic blood pressure readings on the sphygmomanometer should benoted corresponding to the indication of the pulse beats on said'sphygmometer.

4. The method of measuring blood pressure which comprises accuratelyindicating the points of systolic and diastolic blood pressures byimposing the pulse beats of the body upon a crystal microphone placed indirect contact with a person in close proximity to an artery, amplifyingthe electrical variations resulting from the mechanical vibrations ofthe crystal microphone, and visibly indicating the time of occurrenceand intensity of said vibrations to'signify the correct periods forreading said blood pressures.

HARRY R. LIPPI'I'I.

